1. Field of the Invention
The present general inventive concept relates to signal transmission of an electronic device, and more particularly, to a method of reducing an effect of electromagnetic waves which are emitted from a harness that transmits a signal.
2. Description of the Related Art
A high frequency signal flowing along a transmission path radially emits an electromagnetic field. The strength of the electromagnetic field is directly proportional to the power of the signal.
In an electronic device, a plurality of signal lines are used in a harness connected between two connectors in order to electrically connect circuit parts. A harmonic component of the signal transmitted through the harness is emitted, resulting in electromagnetic interference (EMI). The EMI becomes more severe as the frequency of the transmitted signal increases and the length of harness increases.
FIG. 1 is a schematic diagram of a circuit system in a conventional printer system. Referring to FIG. 1, the circuit system includes a power supply unit 102, a laser scanning unit 104, a CCD (charge-coupled device) unit 106, an ADF (auto document feeder) unit 108, and an operation unit 110.
A main controller 102a of the power supply unit 102 is connected to the laser scanning unit 104, the CCD unit 106, the ADF unit 108, and the operation unit 110 by harnesses 122, 124, 126, and 128, respectively.
Several MHz signals and several tens of MHz signals are transmitted through the harnesses 122, 124, 126, and 128. During the transmission of the signals, the harnesses 122, 124, 126, and 128 are main sources of harmonic emission. The harmonic components emitted from the harnesses 122, 124, 126, and 128 have an adverse effect on peripheral electronic devices, and may cause a malfunction of the printer. Therefore, a method of reducing harmonic components emitted through harnesses 122, 124, 126, and 128 is needed.
Conventional methods of reducing harmonic emission from a harness include the use of a ferrite core, the use of LVDS (low voltage differential signaling), and shielding of the whole harness.
Ferrite, which is a magnetic material used to absorb electromagnetic emission from a wire or a cable, is cylindrical, block-shaped, or core-shaped. Signal lines are inserted in or wound around a ferrite core. FIG. 2 is a perspective view of a conventional connector in which a ferrite core 202 is used.
However, when a ferrite core is used, there are disadvantages in that the production cost of a device increases as much as the price of the ferrite core and the length of a harness should be extended according to how many times the harness is wound around the ferrite core. Although the ferrite core can filter different harmonic domains according to the size and material of the ferrite core, if a length of the harness changes, a problem may occur in other frequency domains.
LVDS, in which a signal is converted to a low voltage differential signal and transmitted, has been widely used to prevent electromagnetic interference in printers, laptop computers, and liquid crystal displays (LCD).
FIG. 3 is a block diagram of a conventional circuit to which LVDS is applied. To transmit a signal using LVDS, a transmitting part should include an LVDS transmitter 302 and a receiving part should include an LVDS receiver 304.
While transmitting a signal using LVDS can effectively reduce electromagnetic waves, a large expense is incurred to realize the LVDS, and since LVDS is used for main signal lines, it is difficult to handle the harmonic frequency induced on other signal lines and emitted therefrom.
EMI noise can be diminished by shielding the whole harness with a metal conducting surface which is connected to a ground. However, signal distortion may occur due to a parasitic capacitance between the metal conducting surfaces or between the metal conducting surface and signal lines, and production costs can be increased.